Method of obtaining photographic contrasts



Feb- 1, 1938. J. H. DE BOER :T AL. 2,106,868

ETHOD OF OBTAINING PHOTOGRAPHIC CONTRASTS I Filed Dec. 19, 1934 Patented Feb. 1, 1938 I .UNITED STATES 2,108,868 METHOD F lOBTAINING PHOTOGRAPHIE CONTRA Jan Hendrik de Boer and Klaas Hinderikns Klaassens, Eindhoven, Netherlands, assigner! to N. V. Philips Glceilampenfabrieken, Eindhoven, Netherlands Application December 19, 1934, Serial No. '158,832 In Germany December Z7, 1933 6 Claims.

layer which has been sensitized by means of a naphthalene diazonium compound.

Accordingv to our invention. the formation of- ,photographic contrasts is obtained by means of an actinic exposure of a self-developing layer sensitized by means of a na'phthalene diazonium l0 compound.

In the U. S. patent application Ser. No. 612,36 of De Boer, Dippel and Alink, now Patent No. 2,034,508 there has been described a process using a self-developing light-sensitive material l5 formed of a benzene diazonium compound, which diazonium Vcompound during exposure to light does not form coloring matter, but partly decomposes and the decomposition products, subsequently to the exposure, form with the remaining undecomposed diazonium compoundsl a colored substance.

By the term self-developmen ",'as used herein, is meantpthe propertyofforming, as a result of and subsequently to an exposure to actinic light,v 5 coloring matter by means of the union between the light decomposition product-formed from .a4

diazonium compound in the light sensitive layer during the exposure-and the available excess of diazonium compound; without the addition of any further chemical reagents such as ammonia gas or alkaline solutions, and correspondingly a lightsensitive material having such property, is referred to as self-developing", which promotes the obtention of a minimum moisture content of the layer.

among others that it is not subjected to aftertreatments with solutions offhemical substances 40 for development and fixation, which not only eliminates the expense and work involved in such treatment, but also avoids therisi: of distortion caused by such wet treatments. 1

According to the present invention, instead'of ingthe actual exposure. can be obtained.

43 using benzene diazonium compounds, naphthalene diazonium* compounds are'used as self-developing materials, which compounds, under the conditions more fully to be described hereinafter, give a material of greater stability than can be 'obtained with the self-developing` layer formed with benzenediazonium compounds.

v Ithas already been suggested to usea light- \sensiti`ve layer containing thecompound consist- .l ing of 1-diazonium-2-hydroxynaphthalene-4-mf foacid, sodium carbonate andtartar emetic for` Such a self-developing light-sensitive layer as photographic material has various' advantages, Y

(Cl. -B)

photographic purposes. Thereby, upon exposure, coloring appears on those portions which have been exposed to light and thus negative images are obtained. The exposed materialis subjected to treatment in a diluted aqueous solution of so- .5 dium carbonate. It was found that good printscan not be obtained by this process, as such washing operation causes rtheimage to fade or disappear, not only if the solution is quite dilute, but -even if only water is used. f It has also been suggested to use the above-'- mentioned naphthalene diazonium compound to obtain positives from positives by subjecting the material containing said compound after its exposure-during which exposure itis copied out l5 to daylight with the template removed, and subsequently developing it in alkali.y In this manner a substance, which in alkaline solution unites with the non-converted diazonium compound to form a coloring matter, is produced at such points zo which were not exposed to light when the. original copying out under the positive took place.

Finally'it has been suggested to use the abovementioned naphthalene diazonium compound to obtain an image without the use of'subsequent 25 vchemical treatment. 'I'hereby the-light-sensitive layer was exposed under a template' or tracing, and the so-exposed light-sensitive layer theref .after subjected to further exposure in daylight; with the template or tracing removed therefrom- 30 and then left in a dark place where, and it has j been suggested that after a certain time interval, upon the initially unexposed portions colored matter was automatically formed. However, it

was found that with um, colomrormauon am 35- not take place at all, even if the material kept in the dark for a very longtime f. i. three we eks.

We have found that a close connectionexists between the pH-value of a layer sensitized with a naphthaiene diazonium and theformation of o coloring matter by self-development and that by imparting to the layer a suitable pH4 value, a satisfacto'ry development, in that no or substantially no ormation of coloring takes place dur- According 'to our invention, layers by naphthaiene diazonium compounds and hav.-

ingor being mamedxum having. properly- A upon the moisture content which the lightsensitive layer possesses, or is capable of taking up during the exposure, and that with increasing moisture content the formation speed of coloring matter is increased; furthermore, that to obtain the desired results, the amount of actinic light used for the exposure, the pH value of the light-sensitive layer, and the moisture content of the layer have to be in proper rela-v tionship; this relationship depending upon the specific naphthalene diazonium -compound used.

The invention will be more fully explained in connection with the following example and the drawing forming part of the specification, and in which:

Figure l. is a diagram showing the dependency of the formation speed of the coloring matter upon the pH value (acidity or alkalinity) of the light-sensitive material, and

Fig. 2 is a diagram showing the relation between the intensity of the nal coloring obtained and the amount of actinically acting light striking the light-sensitive layer.

Referring to. Figure l, the abscissae give the pH values of the light-sensitive layer, whereas the ordinates give the corresponding formation speed of the coloring matter.

The curve 8 represents the formation speed of the coloring matter for a given moisture content of the layer and for different pH values (acidities and alkalinities) of the light-sensitive layer.

To obtain the desired contrast effect itis required rst of'all, that during the exposure the image be copied out i. e. that the diazonium compound be decomposed at the exposed portions and, that the speed of decomposition of the diazonium compound be greater, during the exposure than is the speed at which the coloring matter is formed. Secondly, that after the exposure there shall be self-developing, i. e. that coloring matter be formed by undecomposed diazonium compound entering into reaction with the decomposition products of the diazonium compound.

Unless the diazonium compound is photochemically decomposed, evidently no copying out can take place. On the other hand, if the formation speed of the coloring matter is greater than the speed of decomposition, formation of coloring matter takes place with such rapidity during the exposure, that copying out is impossible, even if the most intensive available light sources are'used.

In Fig. 1, the line I0, which is parallel to the abscissa. axis, represents the speed of photochemical decomposition for a given light intensity or actinic light energy falling on the light-sensitive layers during the exposure. The diagram is shown to be divided, according to the pH value of the light-sensitive layer, into three zones `marked A, B and C. Of these zones, zone A extends from the ordinate axis to the ordinate through point I, the latter point falling somewhat to the right of the point I2 (which corresponds to the pH value 'l or chemical neutrality), the point I representing the alkalinity at which the formation speed of coloring matter is rst discernible.

The zone B extends from the ordinate passing l through point I to the ordinate passing through point 2, which latter point is the intersection of the curve 8 with the linev I0, While the zone C extends towards the right of zone B.

It should be well understood that the pH values and the formation speed of the coloring matter are not drawn to scale, and the curves 8 and 9 merely indicate the general character of the -relationship without giving exact values.

Taking rst the zone A, it will be noted that,

with the pH values lying within this zone, the diazonium compound can be photochemically decomposed. However, in this zone no formation of coloring matter can take place either during the actual exposure under the template, or thereafter when keeping the exposed print in the dark, and therefore the zone A is unsuitable for the purpose of the invention.

In zone C the formation speed of the coloring matter is greater than is the. speed of the decomposition of the diazonium compound and therefore the formation of coloring matter takes place so rapidly during the exposure that no copying out is possible, even by means of the most intensive available light sources.

Referring nowto zone B, which extends from layers having slight alkalinity to layers having moderate alkalinity, it will be noted that the formation speed of the coloring matter, while increasing toward the right, remains smaller thanthe speed of photochemical decomposition. Thus, light-sensitive layers having pH values falling within the zone B can be copied out and subsequently produce coloring matter by self-development,

The zone B is, therefore, the only zone which is suitable for the process of the invention and to obtain a reasonable formation speed of the coloring matter it is desirable to work in the right-hand portion of this zone, although preferably staying a reasonable distance to the lef-t of the point 2, as too close an approach to point 2 increases the danger "of coloration during the exposure:

If, instead of the assumed light intensity used during exposure and corresponding to line I0, a higher intensity of exposure yis used, as represented by the dot-and-dash line I3, the useful zone B is extended toward the right, as indicated by the' intersection point I4 of line I3v with curve 8.

As stated, theformation speed of the coloring matter alsodepends upon the quantity of moisture which the light-sensitive layer possesses or is capable of taking up during exposure, and the formation speed decreases with decreasing moisture content and vice versa.

The dotted curve 9 represents the formation speed of the coloring matter for a moisture cori tent 1owe`r` than in the case of curve 8. Thereby as appears from Fig. 1; the curve 9 and line I0 intersect at a point 2' which point lies to the right of point 2; thus the zone B is extended toward the right by using a lower moisture content.

From the above it will be thus noted that the zone B can be extended by using either a higher light intensity for the exposure or a lower moisture content of the light-sensitive layer. However, the extension of the useful zone B is limited Y by the fact that a very high alkalinity will so strongly increase the formation speed of the co1- oring matter as to prevent the possibility of copying out.

The importance of the proper relationship between th`e speed of photochemical decomposition of the diazonium compound and the formation speed of the coloring matter by self-development will further appear from Fig. 2. In this figure curve AIl gives the intensity of the final coloring obtained as a function of the amount of actinically-active light striking the light-sensitive layer during the exposure. Thereby the abscissae give the amount of actinic light and the ordinates the intensity of the resulting-coloring.

In the example given, a positive is made of a tracing whereby, in the print obtained, upon actinic exposure of the light-sensitive layer, the portion corresponding to the lines of the tracing which will remain either unexposed or only slightly exposed to light, appear as colored lines, whilethe blank and thus transparent portions of the tracing will cause the corresponding portions of the print to be fully exposed and thus to appear uncolored. Thus a positive from a positive is obtained.

When the light-sensitive layer is exposed to light under the4 tracing,'it is struck unde'r thev lines of the tracing by a small quantity of light represented by the point 3, to which corresponds the ordinate I5, whereas under the blank or transparent portions-of the tracing the lightsenstive la'yer is struck by a comparatively large amount of light, represented by the point 4 whose ordinate is zero.

The self-development of 'the print may take place in the dark or by subjecting the print, after removal of the tracing, to a slightly actinic light. In this latter case an equal and small amount of light uniformly strikes all of portions of the photographic layer, this amount of light being in.

the total amount of actinic light which strikes the portion to remain uncolored corresponds to the abscissa 5.

It will be seen that the intensities of the final coloring are represented by the ordinate -1 corresponding to the amount of light 6, and is practically zero corresponding to the amount of light 5. It will be thus noted that at the pointsv 4 and 5 the light intensity is so great that the entire diazonium compound becomes decomposed, and

no undecomposed diazonium compound remainsV to form, with the decomposed diazonium compound, coloringimatter.

Instead'of increasing .the intensity of coloring from point l5 to point l by means of afterexposure, this can be also achieved by moderate heating of the layer or by increasing its moisture-content.

From the above it will appear that in case a positive is `to be obtained from a positive, a very definite relationship must exist between the speed of color formation and decomposition, as otherwise the desired sharp contrast eiiect isl not ob'- tained. The -same applies, as will be later pointed-out, when negatives are to be obtained from a positive.

In practice the ideal 'conditions represented by Fig. 2jare not always obtainable, and even on the fully exposed portions of the print a small amount of color formation may take place during the exposure.

the sensitive carrier, for` instance the paper carrying' the light-sensitive substance, is subjected t9. intensive drying in such a manner that the paper retains a moisture content of less than 1%.

B y the degree 'of moisture" of the paper, as

used herein, is to be understoodv here to mean the percentage decrease in weight which airdried paper experiences when it is heated for 24 hours at a temperature of 25 C. within an enclosure dried by fresh phosphorus pentoxide. For a correct understanding, it must be mentioned that drying in an lenclosure kept dry by means of phosphorus pentoxide results in a greater decrease of the moisture content of the paper than the generally used method of drying according to which the paper is heated at comparatively high temperature, say from to 110 C. Thus, for

example, it has been found that so-called airi dry paper, when dried at a temperature up to C. showed a decrease in weight of 61/2%, but

when dried within an enclosure'kept dry by means of posphcruspentoxide is showed a decrease in weight of 7.9%. l

Such intensive drying may also be achieved by subjecting the material to'a ow of 'moisturemoisture by freezing out 'the moisture from the v gas at a very low temperature.

Such intensive drying of photographic material comprising diazonium compounds is described and broadly claimed in the U. S. Patent 1,973,788 to Alink and De Boer. Y

The following specic example will serve to further illustrate the invention:l

Example The sensitized photographic material adapted for making prints from tracings is obtained by soaking a suitable paper carrier in a solution of 1% 1diazlmium-Z-hydroxynaphthalene-i-sulfoacid (1 mol.) +0.6% anhydrous sodium carbonate in water, and by subsequently drying it in air.

To make the print the sensitized paper is exposed under a template, for instance a tracing, for a time interval of about three minutes, and using as a light source, for instance a 5 kw. incandescent `iilament lamp placed at a distance of about 25 cm. from the template.

Immediately after the exposure the image is faintly visible, while the background is uncolored.

The so-exposed paper is then allowed to remain in the dark during which the self-development takes place, which may be accelerated by the presence of water vapor. The self-development may also be accelerated by putting a moistened cloth heated to a temperature of about 100 C. on the paper.

By the above method a positive is obtained from a positive and the image has a brownish-yellow tone. If the quantity of anhydrous sodium carhas been stated before. the sensitized paper is subjected to intensive drying before being used for the exposure. With the moisture content thus minimized, the formation speed of the coloring matter during the exposure is so reduced thatno coloring whatsoever takes place at the lfully exposed portions.

Instead of using sodium carbonate other alkaline agents, especially salts giving slightly alkaline reaction,.are suitable for carrying out the invention, for example, sodium borate (Nemici-10H30),

or sodium phosphate (NaaPO4.10H2O) or sodium selenite (NazSeOa), which in proper amounts,

which of course depends upon their alkaline reaction, will give the light-sensitive layer the desired pH value.

For example for 1 mol. diazonium compoundv 31/2% Na2B4O1.10HzO or 6% NaaPO4`.10H2O or.4% NazSeOs may be used.

It is also possible to obtain by means of the' template will be considerably less and practically zero. The so-exposed print is then subjected to self-development in the dark in the presence of air.

As will appear from Fig. 2, the "exposed porl tions of the print will be now strongly colored, whereas the "unexposed portions will remain substantially colorless.

However, to insure that the available non-decomposed naphthalene diazonium compound remaining at the non-exposed portions of the print does not, by gradual decomposition, cause darkening of the unexposed portions, after the self-developed negative print is removed from the dark, they are rapidly and completely decomposed by a fixation process, consisting in subjecting the print to strongly actinic light without a template, whereby a complete decompositiontakes place at the previously unexposed portions, and so rapidly as to prevent any color formation on these portions.

While we have described our invention in connection with specific examples and in specific applications, we do not wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What we claim is:

l. In the method of producing photographic contrasts by selectively exposing to actinic light a layer sensitized with a naphthalene diazonium compound and forming coloring matter by the union of the diazonium compound and its lightdecomposition product, the step of imparting to said layer prior to exposure a pH value lying within a range having an upper limit corresponding .to the point at which there will be substantially no formation of coloring matter during the exposure and a lower limit greater than '7 and corresponding to the point at which the color formation subsequent to the exposure can be obtained solely by the influence of water and withcait `the addition and removal of any chemical substance.

2. In the production of photographic contrasts by selectively exposing to actinic light a layer sensitized with a naphthalene diazonium compound to partially decompose the compound at selected portions and by forming coloring mat- 'ter by the union of the compound and its light decomposition product, the steps of alkalizing the layer prior to exposure to impart thereto a pI-I value lying within a range having an upper limit corresponding to the point at which there will be substantially no formation of coloring matter during the exposure and a lower limit greater than 7 and corresponding to the point at which subsequent color formation can be obtained solely by the influence of water, and exposing the layer without the formation of pronounced coloring matter.

3. In the method of producing photographic contrasts by selectively exposing to actinic light a layer sensitized with a naphthalene diazonium compound and forming coloring matter by the union of the diazonium compound and its lightdecomposition product, the step of adding an alkaline-reacting salt to said layer to impart thereto a pI-I value lying within a range having an upper limit corresponding to the point at which there will be substantially no formation Vof coloring matter during the exposure and a.

lower limit greater than 'I and corresponding to the point at which the color formation can be. obtained subsequent to the exposure solely by the influence of water and without the addition or removal of any chemical substance.

4. In the method of producing photographic contrasts by selectively exposing to actinic light a layer sensitized with a naphthalene diazonium compound and by forming coloring matter by the union of the diazonium compound and its lightdecomposition product, the steps of imparting to said layer prior to the exposure a pH value lying.

within a range having an upper limit corresponding to the point at which there will be substantially no formation of coloring matter during exposure and a lower limit greater than 7 and corresponding to the point at which the color formation can be obtained solely by the influence of water and Without the addition or removal of any chemical substance, and drying the layer prior to exposure to reduce its moisture content to below 1%.

5. The method of producing photographicprints, comprising the steps sensitizing a layer with a naphthalene diazonium compound, alkalizing the layer to give same a pH value less 'than that value at which there will be substantially no formation of coloring matter during the exposure and more than that value at which the color formation can be obtained solely by the influence of water and without the addition or removal of any chemical substance, drying the layer to reduce its moisture content to below 1%, selectively exposing the layer to actinic light to partially decompose the diazonium compound on selected portions without the formation of appreciable coloring matter, and wet-ironing the exposed layer at .a temperature of about 100 C.

to form coloringmatter at the selected portions by the union ofthe diazonium compound and its .light decomposition product.

6. In producing photographic contrasts by seiectively exposing to actinic light a layer sensitized with a naphthalene diazonium compound and forming contrasts by the union of the diazonium compound and its light-decomposition product, the-steps of alkalizing the unexposed layer to a degree of alkalinity lying within a zone having an upper limit corresponding to the point above which there will be appreciable formation of coloring matter during the exposure and a lower limit corresponding tothe point above which color formation can be obtained subsequent to the exposure solely by the influence of water and without the addition or removal of any chemical substance, andA selectively exposing the layer to partially decompose the compound at selected portions without the formation of appreciable coloring matter during the exposure.

JAN HENDRIK m: BOER.

KLAAS HINDERIKUS KLAASSENS.

. CERTIFICATE CORRECTION. Patent No., 2,106,868. February l, 1958.

JAN HENDRIK de BOER, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows :v Page l, second column, line L15, after thevword and comma "self-development,"insert limited; and that the 'said Letters Patent should be read w ith this correction therein that the-same may conform to the reco'rd of the case in the Patent Office. v

signed and sealed this 15th day of March, A. D. .1958.

Henry Van rsdale,

(Seal) I Acting Commissioner of Patents. 

